Method for producing a flexible circuit configuration

ABSTRACT

A method is specified for the production of a flexible circuit configuration, which allows the manufacturing of such flexible circuits on a carrier film cost-effectively and with high precision. For this purpose, the carrier film is fastened at the beginning of the method on a rigid frame, which encloses an inner area, and spans the inner area using an inner surface. After finishing of a layer structure and optionally additional method steps, structures for flexible circuit configurations which are created over the inner surface may be cut out easily by cutting the flexible circuit configurations out of the inner surface as a cutout. Through the fastening of the carrier film on the frame, it is ensured during the various method steps of the production of the flexible circuit configuration that the carrier film, which is flexible per se, always forms a level foundation for the various method measures, in particular the photolithographic structuring of layers of a layer structure.

CROSS REFERENCE TO RELATED APPLICATIONS

This patent application claims priority of the German patent applicationNo. DE 102010016781.9, filed on 4 May 2010. The entire content of thispriority defining application is incorporated herein by explicitreference for any purpose.

There are two related co-pending US applications which are filed on thesame day as the present application. The first entitled METHOD FORPRODUCING A FLEXIBLE CIRCUIT CONFIGURATION, FLEXIBLE CIRCUITCONFIGURATION, AND ELECTRICAL CIRCUIT CONFIGURATION HAVING SUCH AFLEXIBLE CIRCUIT CONFIGURATION claims the priority of the German patentapplication No. DE 102010016780.0, filed on 4 May 2010. The secondentitled METHOD FOR PRODUCING A FLEXIBLE CIRCUIT CONFIGURATION claimsthe priority of the German patent application No. DE 102010016779.7,filed on 4 May 2010.

FIELD OF THE INVENTION

The invention relates to a method for producing a flexible circuitconfiguration and a manufacturing module of such a method.

BACKGROUND OF THE INVENTION

Flexible circuit configurations are advantageous, inter alia, for use inapplications in which the circuit configuration must have permanentflexible properties, in particular, for example, in body implants or inobjects which have at least limited flexibility in use, such as creditcards.

Flexible circuit configurations contain at least one insulating layerand at least one conductive layer, at least the conductive layer beingstructured in the surface. The terms insulating layer and conductivelayer refer in this case and hereafter to the electrical properties ofthe layer materials. Frequently, at least two structured conductivelayers are provided, which are spaced apart from one another by at leastone insulating layer acting as a separation layer. The two conductivelayers are typically conductively connected to one another in spots viathrough contacts through the separation layer, which is also structuredin the surface for this purpose, so that a three-dimensionalconfiguration of conductor structures arises. The structuring of theconductive layers and the insulating layers is typically performed byphotolithography using different masks.

For a high precision during the structuring of a layer deposited overthe entire surface, which is important in particular in the case of verysmall structure dimensions, the layer structure can be deposited on arigid substrate, for example, on a silicon wafer. After the layerstructure is deposited, optionally after further method steps of theproduction including possible equipment with discrete components on asurface of the flexible circuit configuration, the flexible circuitconfiguration is separated from the substrate. Since the layer structureitself is typically less than 0.1 mm thick, a flexible film can beconnected to the layer structure, which can also have through contacts.The rigid substrate advantageously allows the handling of the circuitconfiguration during the production process, however, the separationfrom the substrate can result in damage of the finished flexible circuitconfiguration because of sensitivity of the layer structure to varioustypical detachment methods.

SUMMARY OF THE INVENTION

The invention is based on the object of specifying a cost-effective andreliable method for producing a flexible circuit configuration. Afurther object of the invention is to specify a manufacturing moduleusable within such a production method.

Solutions according to the invention are described in the independentclaims. The dependent claims contain advantageous embodiments andrefinements of the invention.

In the invention, a carrier film is used as the underlay for thedeposition of the layer structure of the flexible circuit configuration,the carrier film being fastened on a frame which encloses an inner area,which is spanned by the film. The carrier film advantageously has edgesurfaces pressing against the frame in one plane and the inner surfaceof the carrier film spanning the inner area of the frame is essentiallylevel. The film can advantageously be held on the frame under elastictension, which is uniform in the film plane. The layer structure havingthe at least one structured conductive layer for the flexible circuitconfiguration is deposited over the inner surface on the carrier film,one or more layers of the layer structure typically also being depositedover the edge surfaces of the carrier film, but not forming part of theflexible circuit configuration to be produced there and therefore alsonot being understood hereafter as the layer structure of the flexiblecircuit configuration. The creation of the layer structure can also, ina preferred embodiment, comprise at least one method step forsolidifying a material, which is applied in free-flowing form, underelevated temperature, in particular at least 250° C., an electricallyinsulating polyamide layer being producible in particular byimidization. The material of the carrier film advantageously has acoefficient of thermal expansion which differs from the coefficient ofthermal expansion of the frame material by not more than 10 ⁻⁵/K. Theframe material is selected as resistant to chemical, thermal, andmechanical effects during the manufacturing process.

The carrier film can advantageously be fastened on the frame by gluingand/or lamination, the application of contact pressure forces and/orhigher temperatures also being able to be provided. The carrier filmadvantageously comprises a polymer, in particular a polyimide. Thecarrier film can also contain fiber material, such as glass fibers, formechanical reinforcement. The carrier film can also be constructed asmultilayered per se.

After the deposition of the layer structure for the flexible circuitconfiguration on the carrier film, carrier film and layer structure forma flexible solid composite. The thickness of the carrier film isadvantageously greater than the thickness of the layer structure. Thecomposite of carrier film and layer structure can be subjected tofurther method steps, while the carrier film remains fastened unchangedon the frame. Such further method steps may be, for example, creatingcontact surfaces, applying solder bumps, equipping with discretecomponents, etc. A high precision of the orientation of the carrier filmhaving the layer structure can advantageously be reliably ensured in asimple manner not only during the structuring of one or more layers ofthe layer structure but rather also during the mentioned further methodsteps by the dimensional stability of the rigid frame. In particularalso the inner surface of the film, which is not directly connected tothe frame itself, is held in a uniform position with respect to theframe by the fastening of the film on the rigid frame, so that bothdifferent masks for the structuring of different layers may be orientedprecisely relative to previously created structured layers and alsosolder bumps or discrete components may be applied precisely in positionwith respect to previously produced structures. Positioning referencesfor reproducible precise orientation can advantageously be provided forthis purpose on the rigid frame and/or on the edge surface of thecarrier film.

The rigid frame allows the simple handling of the flexible circuitconfiguration during multiple successive manufacturing steps, amanufacturing module which can be handled uniformly, and which containsthe frame and the film fastened thereon having the layer structure, alsobeing transportable between various manufacturing devices ormanufacturing stations. Multiple flexible circuit configurations, whichmay also differ per se, may advantageously be processed over allprocessing steps.

After completion of all manufacturing steps which are to be performedwith the carrier film fastened on the frame, the flexible circuitconfiguration can be cut out from the inner surface over the inner areaas a partial surface, which can be performed in a particularly simplemanner and without danger to the flexible circuit configuration due tothe free spanning, e.g., by stamping or cutting, the latter also using alaser beam.

Advantageously, a rigid inner part can be laid in the inner area of theframe for individual manufacturing steps of the production method, whichforms a mechanical support for the carrier film without being connectedto the carrier film. On the one hand, this can thus prevent the carrierfilm from sagging down in the inner area under its intrinsic weight andmask structures from being imaged fuzzily on the layer to be structuredduring photolithographic structuring. On the other hand, the film havingthe layer structure can reliably support the lower side of the film inparticular during manufacturing steps in which pressure forces areexerted on the side of the layer structure facing away from the carrierfilm and/or the frame. The inner part is preferably produced jointlywith the frame from a flat plate, in that, for example, by laser beamcutting, an inner contour of the frame is created around an inner areaand the cutout surface thus arising is used as the inner part. Frame andinner part advantageously then have equal thicknesses perpendicular tothe plate surface from the beginning. Frame and inner partadvantageously comprise the same material, preferably a stainless steelwhich is insensitive to solvents and temperatures of the variousmanufacturing steps.

The inner surface of the carrier film can advantageously also beprocessed from the side facing toward the inner area of the frame. Inparticular, openings can be produced through the carrier film andthrough contacts can preferably be produced in the openings. Suchopenings are advantageously created in the carrier film after depositingat least one conductive layer over the side of the carrier film facingaway from the frame and/or the inner area and lead up to a conductorsurface of a conductive layer, if necessary, the opening through thecarrier film also being continued through an insulating layer betweencarrier film and a conductive layer. In particular, contact surfaces maybe produced on the side of the carrier film opposite to the layerstructure and facing toward the inner area, which are electricallyconnected via through contacts through the carrier film to at least onestructured conductive layer of the layer structure. The surface facingtoward the inner area can also be metal plated over the entire surface,for example, and form a shielding surface and/or an electrical groundsurface, using which individual conductor surfaces within the layerstructure are contacted via through contacts through the carrier film. Afurther layer structure can also be created on the side of the carrierfilm facing toward the inner area. Finally, it is also possible tocreate the layer structure only on the side of the carrier film facingtoward the inner area.

Multiple flexible circuit configurations may advantageously be producedsimultaneously in a common manufacturing module and subsequently beseparated from the frame and from one another.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in greater detail hereafter on the basis ofpreferred exemplary embodiments with reference to the drawings. In thefigures:

FIG. 1 shows a top view of a manufacturing module,

FIG. 2 shows a side view of FIG. 1,

FIG. 3 shows a frame having cutout inner part,

FIG. 4 shows a first embodiment of a method,

FIG. 5 shows an embodiment having through contacts through the carrierfilm.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the examples described hereafter, the relative dimensions of theindividual components in the drawings are not shown to scale. Inparticular, the thickness of the film and the thickness of the layerstructure or individual layers of the layer structure are shown greatlyexaggerated.

FIG. 1 shows a manufacturing module FM in a view perpendicular to thesurface of a layer structure for flexible circuits. Multiple flexiblecircuits FS are indicated by their contours. In FIG. 2, a sectional sideview of FIG. 1 is shown in a different scale. FIG. 3 shows a preferredproduction of a rigid frame SR, which is used in the method or themanufacturing module, in which a cutout is produced from a closed platesurface along an inner contour IK. During the production of the cutout,an inner part IT arises as the cutout plate section, whose outline Al isless by the cutting width of the cutout than the inner contour IT of therigid frame SR. The inner part IT can therefore be laid unbraced andalso with slight lateral play if needed in the inner area IB, which isenclosed by the inner contour of the frame SR. The frame SR and theinner part IT advantageously have an identical plate thicknessperpendicular to the plate surface. The outer contour of the rigid frameSR is identified by AK. In the outlined example, the rigid frame SR isshown having square inner contour IK and outer contour AK. The rigidframe can also have a different, preferably rotationally-symmetricregular shape such as a rectangular shape or a circular ring shape.

In the manufacturing module FM, a carrier film TF is fastened on a sideof the frame referred to hereafter as the upper side RO, which ispreferably glued and/or laminated on the upper side RO of the frame SR,during the fastening of the carrier film TF, the film preferably beingelastically pre-tensioned isotropically on all sides in the film plane.During the fastening of the carrier film TF on the upper side RO of theframe SR, mechanical surface contact pressure and/or elevatedtemperature may be applied. The carrier film TF is fastened using anedge surface area RF on the rigid frame SR and its inner surface IFspans the inner area delimited by the inner contour IK of the frame SR.A lower side FU of the carrier film TF faces toward the inner area IB. Alayer structure SA is deposited on the upper side FO of the carrierfilm, facing toward the frame SR or the inner area IB, which has atleast one conductive layer, which is structured in the surface, made ofan electrically conductive material, in particular a metal. The layerstructure forms structures of flexible circuit configurations over theinner surface IF of the carrier film TF. In FIG. 1, multiple suchflexible circuit configurations FS over the inner surface IF of thecarrier film are shown by their contours. Advantageously, multiple suchflexible circuits FS may be produced simultaneously and cost-effectivelyover a common carrier film as the underlay. After production of thelayer structure SA for the structures of the flexible circuitconfiguration over the inner surface IF and optionally further methodsteps, such as implementing contact surfaces and/or equipping withdiscrete components, the one or typically the multiple flexible circuitconfigurations FS may be cut out of the inner surface IF, for whichpurpose a cutting tool TW is indicated as representative in FIG. 2. Forsuch cutting of one or more flexible circuit configurations FS out ofthe composite of carrier film TF and layer structure SA in the area ofthe inner surface IF, mechanical cutting tools, stamping tools, or afocused laser beam along the contour of a flexible circuit configurationmay be used, for example.

At 0.3-5 mm, the thickness of the frame is typically a multiple of thethickness of the carrier film, which, at 0.01-0.2 mm, is in turnsubstantially greater than the layer thicknesses of individual layers ofthe layer structure at 0.001-0.01 mm.

FIG. 4 shows individual method steps of a preferred embodiment of theproduction method according to the invention. In FIG. 4(A), the rigidframe SR is laid on an indicated support surface AT, such as aworktable, and a carrier film TF has its lower side FU facing toward theupper side RO of the frame SR. The carrier film TF is applied,advantageously with elastic pre-tension in the film plane, using itslower side FU to the upper side RO of the frame SR and fastened to theframe, in the case of gluing as the type of fastening, the lower side FUof the film and/or the upper side RO of the frame SR being able to becoated using an adhesive material. The inner area IB inside the frame SRis free and the film TF fastened on the upper side RO of the framefreely spans this inner area IB using its inner surface IF.

After fastening of the film having edge surfaces RF on the upper side ROof the frame SR, as indicated in FIG. 4( b), parts of the carrier filmprotruding beyond the outer contour AK of the frame SR can be removed.

For further method steps, the inner part IT shown in FIG. 3 canadvantageously be laid in the inner area IB of the frame SR. When theframe SR and the inner part IT are supported on a common level supportsurface AT, the upper side of the inner part IT facing away from thesupport surface AT is in a common plane with the upper side RO of theframe SR. The carrier film, which spans the inner area IB using itsinner surface IF, can thus advantageously be supported from below andoffer a uniform level upper side FO for further method steps.

In following method steps, at least one, preferably multiple layers aredeposited on the upper side FO of carrier film TF, of which a firstlayer 51 is shown in FIG. 4(B).

In FIG. 4(C), a finished layer structure SA on the upper side FO of thecarrier film TF is assumed. The layer structure contains multipleindividual layers, of which at least one layer is a flatly structuredconductive layer. It is additionally provided in FIG. 4(C) that aninsulating layer is deposited over terminal surfaces AF implemented in astructured conductive layer. Contact surfaces KP, which are located onthe upper side OS of the layer structure, are electrically connected tothe terminal surfaces AF via through contacts through openings in thisinsulating layer. The contact surfaces KP may be used, for example, fordiscrete components to be connected to the flexible circuitconfiguration, for applying solder bumps, for contacting bonding wires,or for soldering the flexible circuit configuration to counter surfacesof the circuit board. Through the support of the lower side FU of thecarrier film TF by the inner part IT, as long as the flexible circuitconfiguration is fastened as part of the composite of the carrier filmTF to the layer structure SA on the frame SR, method steps havingmechanical effect may also occur on the upper side OS of the layerstructure.

In particular, however, it is ensured by the fastening of the carrierfilm TF on the rigid frame SR during the production method that nodistortion of the film having layers of the layer structure depositedthereon occurs and therefore different surface structures, which areproduced in successive method steps in successive layers, are eachoriented precisely and correctly relative to one another. An orientationwithin a manufacturing device can particularly be provided bypositioning references at or on the rigid frame SR and/or the edgesurface area of the carrier film which is fixedly connected to theframe. Through such positioning references, a manufacturing module canalso be removed from a manufacturing device readily between variousmethod steps of the production method and also exchanged between variousmanufacturing devices. In particular a manufacturing module of the typeshown in FIG. 1 can also be relayed, as an intermediate product of aproducer creating the layer structure SA on the carrier film TF forfurther processing up to the finished flexible circuit configuration, toa second producer. Such a manufacturing module can therefore represent aunit which can be handled independently. The inner part IT isadvantageously a component of the manufacturing module.

A variant of a production method is outlined in FIG. 5, in whichterminal surfaces VA are created in a layer directly on or close to theupper side FO of a carrier film TF in a layer structure SV, which isdeposited on the upper side FO of a carrier film TF. After production ofthe terminal surfaces VA, preferably after production of the entirelayer structure SV optionally having further layers, the manufacturingmodule having the side OV of the layer structure facing away from theframe SR, is laid inverted on a support AT, so that the free inner areaIB faces away from the support AT.

Perforations DG are created through the carrier film through the innerarea IB from the lower side FU of the carrier film TF, which extend upto the terminal surfaces VA in the layer structure. The perforations DGare therefore also continued through layers of the layer structureoptionally lying between the carrier film and the terminal surfaces VA.The production of such perforations can be performed by photolithographyor, as indicated in FIG. 5, preferably using a focused laser beam LS,which ablates material in spots from the carrier film TF and optionallylayers of the layer structure SV.

Through contacts may then be produced by metal deposition in theperforations DG from the lower side FU of the carrier film up to theterminal surfaces VA of the layer structure. Such perforations mayparticularly be used for the purpose, in the case of metal plating overthe entire surface on the lower side FU of the carrier film, of settingthe terminal surfaces VA, which are contacted through the throughcontacts through the perforations DG, to a common potential. In anotherembodiment, contact surfaces VP may be created on the lower side FU ofthe carrier film by structured deposition of conductor material, inparticular metal, which contact surfaces are connected individually orin groups to terminal surfaces VA of the layer structure via the throughcontacts through the perforations DG. Such contact surfaces VP may beprovided for the same functions as the contact surfaces KP according toFIG. 4 (C).

The features specified above and in the claims and the features whichcan be inferred from the drawings can be implemented advantageously bothindividually and also in various combinations. The invention is notrestricted to the described exemplary embodiments, but rather can bealtered in many ways in the scope of knowledge in the art.

1. A method for producing a flexible circuit configuration, a layerstructure having at least one structured conductive layer beingdeposited over an underlay, characterized in that a flexible carrierfilm is used as the underlay, the carrier film is connected to adimensionally-stable frame, which encloses an inner area, beforedeposition of the layer structure, the carrier film being connected tothe frame using an edge area and spanning the inner area using an innersurface, the layer structure is created over the inner surface, and theflexible circuit configuration is cut out as a planar part of thecomposite of the first film having the layer structure from the innersurface.
 2. The method according to claim 1, wherein the carrier film isglued to the frame.
 3. The method according to claim 1, wherein thecarrier film is connected to the frame under elastic tension.
 4. Themethod according to claim 1, wherein the carrier film comprises apolymer, in particular a polyimide.
 5. The method according to claim 1,wherein at least one insulating layer is deposited in the layerstructure in addition to the at least one structured conductive layer.6. The method according to claim 1, wherein a layer structure is onlycreated on one side, in particular the side of the carrier film facingaway from the frame.
 7. The method according to claim 1, wherein a layerstructure having at least one structured conductor film is created ineach case on both sides of the carrier film.
 8. The method according toclaim 1, wherein openings are created through the carrier film up to theat least one structured conductive layer.
 9. The method according toclaim 8, wherein through contacts are created through the openings up toat least one conductive layer of the layer structure.
 10. The methodaccording to claim 1, wherein a further film is fastened as a cover filmon the side of the layer structure facing away from the carrier film.11. The method according to claim 10, wherein openings are created inthe cover film which is fastened on the layer structure.
 12. The methodaccording to claim 11, wherein through contacts are created through theopenings of the cover film up to at least one conductive layer.
 13. Themethod according to claim 1, wherein an inner part, which fills up theinner area, is laid in the inner area without connection to the carrierfilm during at least one method step and supports the carrier film. 14.The method according to claim 13, wherein the inner part and the frameare produced from a smooth plate, in that the inner part is cut out ofthe plate.
 15. The method according to claim 1, wherein the framecomprises metal, in particular stainless steel.
 16. A manufacturingmodule in a method for producing a flexible circuit configuration, whichhas a layer structure having at least one structured conductive layer ona flexible carrier film, characterized in that the carrier film isfastened using an edge area on a frame and spans an inner area enclosedby the frame and the layer structure for the flexible circuitconfiguration lies on the carrier film over the inner area.
 17. Themanufacturing module according to claim 16, wherein an inner part whichcan be laid in the inner area is part of the manufacturing module. 18.The manufacturing module according to claim 17, wherein the frame andthe inner part have the same thickness.
 19. The manufacturing moduleaccording to claim 17, wherein the frame and the inner part comprise thesame material.
 20. The manufacturing module according to claim 19,wherein frame and inner part comprise stainless steel.